When Alex(Justin Chambers) walks in on Meredith(Ellen Pompeo) and Cristina(Sandra Oh) lying in a hospital bed, you can briefly see that Ellen is pregnant with her daughter Stella.
First appearances of Jackson Avery and April Kepner.
The storyline about Dr. Bailey's patient, Sarah Freemont, continues in the Private Practice episode, "Right Here, Right Now" (Season 3, Episode 3)
It's revealed that Callie's father's name is Carlos.